JP7697236B2 - Estimation device, computer program, and estimation method - Google Patents

Description

The present invention relates to an estimation device, a computer program, and an estimation method.

To construct a battery module from multiple cells (single cells), there are two methods: applying pressure to the long sides of the multiple cells facing each other, and arranging the multiple cells facing each other without applying pressure. In the latter case, there is a possibility that the cell casing will swell as the battery module is used (charged and discharged).

Patent document 1 discloses an electronic device that detects the degree of expansion of a secondary battery using an expansion detection means attached to the secondary battery and warns the user to prevent damage or performance degradation due to the expansion of the secondary battery.

JP 2014-17141 A

The swelling of energy storage elements such as secondary batteries is thought to be mainly caused by changes in the element structure inside the energy storage element and gas generation. In order to prevent damage to the battery module due to swelling of the energy storage element, or to understand the state changes and deterioration that accompany swelling of the energy storage element, it is necessary to consider the physical phenomena inside the energy storage element. For example, to support model-based development, it is necessary to properly estimate the shape changes of the energy storage element, taking into account the physical phenomena inside the element.

The present invention aims to provide an estimation device, a computer program, and an estimation method for estimating changes in the shape of a storage element.

The estimation device according to one aspect of the present invention includes a determination unit that determines whether the shape change mode of the storage element is a first mode or a second mode, and an estimation unit that estimates the shape change of the storage element according to the shape change mode determined by the determination unit.

According to the above aspect, it is possible to accurately estimate the shape change of the storage element.

FIG. 2 is a perspective view of a battery module. FIG. 11A and 11B are diagrams showing the relationship between the change in cell thickness and the change in element structure. 1 is a diagram illustrating a simulated quarter cross section of one of the wound electrode bodies housed in a cell case. FIG. FIG. 13 is a diagram showing simulation results and actual measured values of the change in cell thickness. 11A and 11B are diagrams showing the relationship between the occurrence of wrinkles in an element structure and the transition of a shape change mode. FIG. 13 is a diagram showing a simulation result of the transition of the long side load. FIG. 1 is a diagram illustrating a configuration of an estimation device. 11A and 11B are diagrams illustrating a method for estimating a change in shape of an electric storage element when left unused (when no current is applied). 11A and 11B are diagrams illustrating a method for estimating a change in shape of an energy storage element when a current is applied. FIG. 4 is a graph showing the relationship between the first mode thermal expansion coefficient and the second mode thermal expansion coefficient and temperature. FIG. 11 is a diagram showing the relationship between the first mode temporal expansion coefficient and the second mode temporal expansion coefficient and ΔSOC. FIG. 11 is a diagram showing the relationship between the first mode temporal expansion coefficient and the second mode temporal expansion coefficient and the central SOC. 13 is a flowchart showing a processing procedure of shape estimation by the estimation device.

The estimation device includes a determination unit that determines whether the shape change mode of the storage element is a first mode or a second mode, and an estimation unit that estimates the shape change of the storage element according to the shape change mode determined by the determination unit.

The computer program causes the computer to execute a process to determine whether the shape change mode of the storage element is the first mode or the second mode, and to estimate the shape change of the storage element according to the determined shape change mode.

The estimation method determines whether the shape change mode of the storage element is the first mode or the second mode, and estimates the shape change of the storage element according to the determined shape change mode.

The determination unit of the above-described estimation device determines whether the shape change mode of the energy storage element is the first mode or the second mode.
The present inventor has found that there are at least two modes of shape change of the electric storage element. Specifically, the present inventor has found that there are at least two modes of shape change of the electric storage element as a dominant factor of the shape change of the electrode body (element). The determination unit determines whether the shape change mode of the electric storage element is the first mode or the second mode based on a predetermined condition.

The estimation unit estimates the shape change of the storage element according to the shape change mode determined by the determination unit. By preparing in advance a shape change estimation method for the storage element for each shape change mode, the optimal method can be adopted according to the shape change mode, and the shape change of the storage element can be accurately estimated.

The storage element may have a wound electrode body.

As described below, the inventors have discovered that an energy storage element having a wound electrode body exhibits a unique shape change mode. By understanding the shape change mode of an energy storage element having a wound electrode body, the shape change can be estimated with high accuracy. Alternatively, the energy storage element may have a stacked electrode body.

The estimation device may estimate that the speed of shape change in the second mode transitioned from the first mode is greater than the speed of shape change in the first mode.

The shape change rate can be expressed, for example, as (amount of shape change/time) or (amount of shape change/total SOC fluctuation). With the above-described configuration, the shape change of the storage element can be accurately estimated both before and after the mode transition.

The estimation device may include a first acquisition unit that acquires or calculates an elapsed parameter related to the elapsed time of the storage element, and the determination unit may determine the shape change mode based on the elapsed parameter acquired or calculated by the first acquisition unit.

The elapsed parameter related to the elapsed period of the storage element may be a parameter for determining whether the shape change mode of the storage element is the first mode or the second mode. With the above-mentioned configuration, the shape change of the storage element can be estimated with high accuracy.

The estimation device may include a second acquisition unit that acquires or calculates a progress parameter related to the flow of current through the storage element, and the determination unit may determine the shape change mode based on the progress parameter acquired or calculated by the second acquisition unit.

The progress parameter related to the flow of current through the storage element may be a parameter for determining whether the shape change mode of the storage element is the first mode or the second mode. With the above-described configuration, the shape change of the storage element can be estimated with high accuracy.

The elapsed parameters may include any one of the number of days that the storage element has been de-energized or energized, the absolute value of the dimensions of the storage element, the amount of change in the shape of the storage element, and the total SOC fluctuation of the storage element.

For example, by formulating the shape change as a function of time in advance, it is possible to obtain the value of the shape change according to time (number of days elapsed). If the number of days elapsed is equal to or less than a threshold, it is possible to determine that the shape change mode is the first mode, and if the number of days elapsed exceeds the threshold, it is possible to determine that the shape change mode is the second mode. The function indicating the shape change differs between the first mode and the second mode.
The progress parameter may be an absolute value of the dimension of the storage element, a change in shape, or a total SOC fluctuation. If the absolute value of the dimension or the change in shape is equal to or less than a threshold, the shape change mode is determined to be the first mode, and if the absolute value of the dimension or the change in shape exceeds the threshold, the shape change mode is determined to be the second mode. Alternatively, if the total SOC fluctuation of the storage element exceeds a threshold, the shape change mode is determined to be the second mode.

The determination unit may determine the transition from the first mode to the second mode depending on the type of at least one of the positive electrode active material and the negative electrode active material of the storage element.

In the case of a lithium-ion battery, lithium ions are inserted into or removed from the active material during charging and discharging. The speed of shape change differs depending on whether at least one of the positive and negative active materials is an active material that undergoes a large or small volume change upon insertion and removal. Therefore, it is preferable to determine the transition from the first mode to the second mode depending on the type of active material. It is believed that energy storage elements with different active materials will have different transition times from the first mode to the second mode even if they are used in the same environment, have the same dimensions, or have the same element structure.

The shape change may include a change in thickness of the wound electrode body.

The thickness direction is a direction perpendicular to the winding axis direction of the wound electrode body (a direction perpendicular to the long side of the energy storage element). As described below, the inventors have discovered that the wound electrode body exhibits a unique shape change mode in its thickness direction. With the above-mentioned configuration, the thickness change of the energy storage element can be accurately estimated.

Below, embodiments of the estimation device, computer program, and estimation method will be described with reference to the drawings.

Figure 1 is a perspective view of a battery module (energy storage device) 10. The battery module 10 includes a rectangular parallelepiped case 11 and a number of cells (energy storage elements) 20 housed in the case 11 in an uncompressed state.

The cell 20 includes a rectangular (prismatic) cell case 21, a cover plate 22, terminals 23 and 26 provided on the cover plate 22, a burst valve 24, and an electrode body 25. The terminals 23 and 26 may be welded terminals as shown in FIG. 1, or bolt terminals as shown in FIG. 2. The electrode body 25 is also called an element, and the wound electrode body is formed by stacking a positive electrode plate, a separator, and a negative electrode plate and winding them into a flat shape. The vertically wound electrode body 25 is housed in the cell case 21 with its winding axis direction parallel to the cover plate 22. The horizontally wound electrode body 25 is housed in the cell case 21 with its winding axis direction perpendicular to the cover plate 22. Alternatively, the electrode body 25 may be a laminated electrode body.

The positive electrode plate is a positive electrode substrate foil, which is a plate-shaped (sheet-shaped) or long strip-shaped metal foil made of aluminum, aluminum alloy, etc., on which an active material layer is formed. The negative electrode plate is a negative electrode substrate foil, which is a plate-shaped (sheet-shaped) or long strip-shaped metal foil made of copper, copper alloy, etc., on which an active material layer is formed. The separator is a microporous sheet made of synthetic resin.

The positive electrode active material may be, for example, a material capable of absorbing and releasing Li, such as lithium transition metal oxides (Li1+ _aMeO2 , a≧1, Me: containing one or more transition metal elements such as Ni, Mn, Co, etc.) such as lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel cobalt aluminum oxide, _spinel type lithium manganate ( _LiMe2O4 : Me is one or more metal elements including at least Mn), lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, etc. Two or more of these may be used in combination.

The negative electrode active material may be, for example, a material capable of absorbing and releasing Li, such as graphite, hard carbon, soft carbon, metallic Li, silicon monoxide, silicon or its alloy, tin or its alloy, lithium vanadate, tungsten oxide, titanium oxide, or niobium oxide. Two or more of these may be used in combination. The present invention can be applied as long as either the positive electrode active material or the negative electrode active material expands during charging and discharging.

The adjacent terminals 23, 26 of adjacent cells 20 in the battery module 10 are electrically connected by a bus bar 12, so that the cells 20 are connected in series. The terminals 23, 26 of the cells 20 at both ends of the battery module 10 are provided with leads 14, 13 for extracting power.

Figure 2 is a perspective view of cell 20. Cell case 21 has opposing long sides 21a, 21b and opposing short sides 21c, 21d. The dimension between long sides 21a, 21b, indicated by the symbol D, is referred to as the thickness, and the dimension between short sides 21c, 21d, indicated by the symbol L, is referred to as the length. Length L > thickness D. In this embodiment, the change in shape of cell 20 (energy storage element) is mainly assumed to be a change in thickness D.

The inventors have hypothesized that there are at least two modes of change in the shape of the cell 20 (mainly the change in thickness D), and have found that this hypothesis is correct. The details are explained below.

Figure 3 is a diagram showing the relationship between the change in thickness of the cell 20 and the change in the element structure. Figure 3A is a chart showing the change in thickness during a storage test. The state of charge (SOC) of the cell 20 was set to 100%, and the cell was left in an environment at a temperature of 55°C, and the change in thickness D was measured. The horizontal axis shows time (days), and the vertical axis shows the increase rate (%) of the thickness of the cell 20. Time t0 is the start time of the storage test. As shown in Figure 3A, the increase rate of the thickness of the cell 20 changes around time t1. Specifically, the rate of change in thickness after time t1 (from time t1 to time t2) is greater than the rate of change in thickness from time t0 to time t1. In other words, the change in shape of the cell 20 progresses in two stages.

Figure 3B is a chart showing the progress of the element structure of the cell 20 (in this embodiment, two vertically wound electrode bodies housed in a cell case and arranged in close proximity), and the three charts show the state inside the cell case at times t0, t1, and t2 in Figure 3A. The line indicated by the symbol W indicates a slit present at the beginning of the winding of the innermost circumference of the electrode body 25. The slit W looks like a thin line in the cross-sectional view as in Figure 3B. The slit W extends in the winding axis direction (perpendicular to the paper surface of Figure 3B). At time t0, the slit W is straight. From time t0 to time t1, the thickness of the cell 20 increases, and at time t1, wrinkles are generated inside the element structure and the slit W is bent. In addition, the outermost circumference of the electrode body 25 bulges. Furthermore, after time t1, the rate of change in thickness increases, the wrinkles inside the element structure become even larger, and the deformation of the slit W also becomes larger. The outermost periphery of the electrode body 25 is further expanded.

Figure 4 shows the results of a CAE (Computer Aided Engineering) simulation to determine why the shape change of the cell 20 progresses in two stages.

Figure 4 is a diagram simulating a 1/4 cross section of one of the wound electrode bodies housed in the cell case 21. In FIG. 4, reference numeral 201 denotes a separator, reference numeral 202 denotes a positive electrode, and reference numeral 203 denotes a negative electrode. The element structure in the cell case 21 is a positive electrode 202, a separator 201, and a negative electrode 203 that are stacked and wound. Such a 2DCAE model (two-dimensional CAE model) was created based on the physical properties (e.g., thickness, Young's modulus, Poisson's ratio, linear expansion coefficient, yield strength, etc.) of the cell case 21 and the materials (separator, positive and negative electrode composite, foil, etc.) that constitute the element structure, and the design values. The expansion of the element structure was reproduced by increasing the thickness of the positive and negative electrode composite (e.g., using the thickness increase transition of the actual measured value). Figures 4A, 4B, and 4C show cross sections of the element structure at times (elapsed time) t = 0, t = tb, and t = tc, respectively. As shown in Figure 4, wrinkles appear in the element structure around time t = tb. Then, from time t = tb to time t = tc, the deformation gradually increases.

Figure 5 shows the simulation results and actual measured values of the change in thickness of cell 20. In the simulation results shown in Figure 5A, the horizontal axis indicates the expansion of the positive and negative electrode composite materials (%), and the vertical axis indicates the cell thickness. In Figure 5A, the points indicated with the letters A, B, and C correspond to the states of the element structures in Figures 4A, 4B, and 4C, respectively. In the actual measured values shown in Figure 5B (storage test at SOC 100% and temperature 45°C), the horizontal axis indicates time (days), and the vertical axis indicates the cell thickness. In Figure 5B, the points indicated with dots indicate the actual measured values.

The simulation results, like the actual measurements, show that the swelling mode (shape change mode) changes at the boundary of the cell swelling change point. In other words, the shape change rate after the change point is greater than the shape change rate in the shape change mode (also called the "first mode") from the initial stage to the change point. This suggests that the change in the rate of increase in cell thickness (shape change rate) is due to the expansion of the element structure. This suggests that there are at least two modes of shape change in part (mainly the positive and negative electrode composites) of the element structure of the energy storage element (e.g., positive and negative electrode composites, positive and negative electrode current collectors, separators, etc.).

Next, we consider the relationship between the occurrence of wrinkles and changes in the shape change mode.

Figure 6 shows the relationship between the occurrence of wrinkles in the element structure and the transition of the shape change mode. Figure 6A shows the element structure from the initial stage to near the change point of the cell swelling (when the shape change mode is the first mode), and Figure 6B shows the element structure after the change point of the cell swelling (when the shape change mode is the second mode). As mentioned above, the electrode body 25 is wound by overlapping the positive electrode, negative electrode, and separator on a flat plate called a winding core, and the winding core is removed when winding is completed. This leaves a straight slit in the center.

As shown in FIG. 6A, when the cell 20 is left alone or electrified (charged and/or discharged) and time passes, the positive and negative electrodes gradually expand. As a result, the electrode body 25 tries to expand outward. Meanwhile, the circumference of the outermost part of the electrode body 25 does not change. When the positive and negative electrodes expand, a reaction occurs in the circular arc portion (rounded portion, R portion), and the positive and/or negative plate (also called "plate") is pushed inward. As a result, the flat portion of the electrode body 25 is pushed outward (first mode).

As shown in Figure 6B, as time passes, the plate continues to be pushed inward by the reaction at the R portion, and the only way for the plate to escape from expansion is toward the flat portion, causing the plate to begin to bend and wrinkles to form. The occurrence of wrinkles makes the plate more likely to bend, and the rate of change in shape (change in thickness) increases (second mode).

Figure 7 shows the results of a simulation of the transition of the long side load. In Figure 7, the horizontal axis shows the expansion (%) of the positive and negative electrode composite material, and the vertical axis shows the cell thickness and the long side load. The long side load is the load when the flat portion of the electrode body 25 is pressed outward in Figure 6. As shown in Figure 7, the change mode of the load that the electrode body 25 applies to the long side of the cell case 21 also changes before and after the point at which the cell bulge changes.

Here, we have described prediction of shape change of an energy storage element, taking into account the change in the swelling mode from the first mode to the second mode depending on the degree of wrinkle formation of the electrode body, using the swelling of a cell having a wound electrode body as an example. Alternatively, the present invention can also be applied to cases where the swelling mode (shape change mode) of the electrode changes in a cell having a stacked electrode body (for example, when the active material is gradually pulverized with charging and discharging, increasing the specific surface area, and changing the amount of deposits formed on the electrode and the mode of gas generation inside the battery).

Next, we will explain the configuration of the estimation device.

Figure 8 is a diagram showing the configuration of the estimation device 50. The estimation device 50 includes a control unit 51 that controls the entire device, an input unit 52, a memory unit 53, a timing unit 54, an output unit 55, a determination unit 56, an estimation unit 57, and a communication unit 58. The control unit 51 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The memory unit 53 is composed of a hard disk or semiconductor memory, etc., and stores required data.

The input unit 52 acquires time series data of a storage element (e.g., cell 20) for which a shape change is to be estimated. There may be multiple storage elements. The time series data includes, for example, time series data of the voltage, current, and temperature of the storage element. The input unit 52 acquires time data in addition to the time series data. The time data may be data indicating the start and end points of the estimation period for estimating the shape change. When the storage element is left unused, the input unit 52 only needs to acquire time data, and when the storage element is in a conducting state, the input unit 52 acquires time series data within the estimation period together with the time data. The time series data may be actual measured values or calculated values. The data acquired by the input unit 52 may be stored in the memory unit 53.

The control unit 51 determines the ΔSOC (State Of Charge) and central SOC of the storage element based on the time series data acquired by the input unit 52. ΔSOC is the difference between the maximum and minimum values of the SOC that changes based on charging or discharging the storage element. The central SOC is the average of the changing SOC.

The timing unit 54 counts the elapsed time when estimating the change in shape of the storage element.

The determination unit 56 determines whether the shape change mode of the storage element is the first mode or the second mode. Specifically, the determination unit 56 determines whether the shape change mode of the storage element is the first mode or the second mode based on a predetermined condition.

The estimation unit 57 estimates the shape change of the storage element according to the shape change mode determined by the determination unit 56. By preparing in advance a shape change estimation method for the storage element for each shape change mode, it is possible to adopt the most suitable method according to the shape change mode, and to accurately estimate the shape change of the storage element.

The output unit 55 outputs the estimation result by the estimation unit 57 to an external device (e.g., a display device, a printing device, etc.).

The communication unit 58 includes a necessary communication module and transmits and receives data and information to and from external devices. For example, it receives and updates an application (program) that specifies the processing of the estimation device 50, and receives and updates the expansion coefficients described below.

The estimation of shape changes in the storage element is explained in detail below.

The inventors have discovered that an energy storage element having a wound electrode body exhibits a unique shape change mode. By understanding the shape change mode of an energy storage element having a wound electrode body, the shape change can be accurately estimated. From the initial stage to the mode transition point (the point at which the cell bulge changes), the shape of the energy storage element changes according to the first mode, and thereafter the shape of the energy storage element changes according to the second mode. The shape change of the energy storage element is appropriately estimated depending on whether the estimation point is before or after the mode transition point.

The speed of shape change in the second mode transitioned from the first mode may be estimated to be greater than the speed of shape change in the first mode. The speed of shape change can be expressed, for example, as (amount of shape change/time) or (amount of shape change/total SOC fluctuation). With this configuration, the shape change of the storage element can be accurately estimated both before and after the mode transition.

9 is a diagram showing a method for estimating the shape change of a storage element when left unused. In FIG. 9, the horizontal axis indicates time (elapsed time) (days), and the vertical axis indicates the cell thickness D. The cell thickness D is the thickness of the cell case (see FIG. 2). Alternatively, the vertical axis may be the amount of change in the cell thickness or the rate of change in the cell thickness. The first mode temporal expansion coefficient K1 represents the slope of the straight line shown by the solid line, and the second mode temporal expansion coefficient K2 represents the slope of the straight line shown by the dashed line. The cell thickness D in the first mode can be calculated by the function F1, such as D=F1(K1, t). Here, K1 is the first mode temporal expansion coefficient, and t represents time. The cell thickness D in the second mode can be calculated by the function F2, such as D=F2(K2, t). Here, K2 is the second mode temporal expansion coefficient, and t represents time. Function F1 (or first mode temporal expansion coefficient K1) and function F2 (or second mode temporal expansion coefficient K2) may be stored in the storage unit 53. Alternatively, functions F1 and F2 may be configured by a calculation circuit.

In the initial stage of estimating the shape change, the estimation unit 57 uses the function F1 to calculate the thickness D of the cell. Here, the variable t of the function F1 and the value D obtained by the function F1 are referred to as the elapsed parameters. In other words, the estimation unit 57 estimates the shape change of the energy storage element over time and simultaneously calculates the elapsed parameters.

The determination unit 56 determines the shape change mode based on the elapsed parameter calculated by the estimation unit 57 and a predetermined threshold value. The elapsed parameter may be any parameter for determining whether the shape change mode of the storage element is the first mode or the second mode. In the example of FIG. 9, the elapsed time t may be used, or the cell thickness D may be used. The cell thickness D may be the thickness itself (absolute value) or the amount of change from the initial thickness value. With this configuration, for example, the shape change of the storage element in an unused state (when not energized) can be accurately estimated.

As shown in FIG. 9, when the elapsed time is equal to or greater than the threshold value, or when the cell thickness is equal to or greater than the threshold value, the estimation unit 57 uses the function F2 to calculate the cell thickness D. With this configuration, for example, it is possible to accurately estimate the change in shape of the storage element when it is left unused (when not energized).

Figure 10 is a diagram showing a method for estimating the shape change of a storage element when energized. In Figure 10, the horizontal axis indicates time (elapsed time) (days), and the vertical axis indicates the cell thickness D. Alternatively, the horizontal axis may be the total SOC fluctuation amount (%). The first mode energization expansion coefficient M1 represents the slope of the straight line shown by the solid line, and the second mode energization expansion coefficient M2 represents the slope of the straight line shown by the dashed line. The cell thickness D in the first mode can be calculated by the function G1 as D = G1 (M1, t). Here, M1 is the first mode energization expansion coefficient, and t represents time. The cell thickness D in the second mode can be calculated by the function G2 as D = G2 (M2, t). Here, M2 is the second mode energization expansion coefficient, and t represents time. The function G1 (or the first mode current expansion coefficient M1) and the function G2 (or the second mode current expansion coefficient M2) may be stored in the storage unit 53. Alternatively, the functions G1 and G2 may be configured by a calculation circuit.

In the initial stage of estimating the shape change, the estimation unit 57 uses the function G1 to calculate the thickness D of the cell. Here, the variable t of the function G1 and the value D obtained by the function G1 are referred to as the elapsed parameter. In other words, the estimation unit 57 estimates the shape change of the storage element over time and simultaneously calculates the elapsed parameter.

The determination unit 56 determines the shape change mode based on the elapsed parameter calculated by the estimation unit 57 and a predetermined threshold value. The elapsed parameter may be any parameter for determining whether the shape change mode of the storage element is the first mode or the second mode. In the example of FIG. 10, the elapsed time t may be used, or the cell thickness D may be used. The cell thickness D may be the thickness itself (absolute value) or the amount of change from the initial thickness value. With this configuration, for example, it is possible to accurately estimate the shape change of the storage element when current is applied.

As shown in FIG. 10, when the elapsed time is equal to or greater than a threshold value, or when the cell thickness is equal to or greater than a threshold value, the estimation unit 57 uses the function G2 to calculate the cell thickness D. With this configuration, for example, it is possible to accurately estimate the change in shape of the storage element when current is applied.

11 is a diagram showing the relationship between the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 and temperature. In FIG. 11, the horizontal axis indicates time (days), and the vertical axis indicates the change in cell thickness (%). FIG. 11 shows a solid line with a slope of the first mode temporal expansion coefficient K1 at temperatures T1 and T2 (>T1), and a dashed line with a slope of the second mode temporal expansion coefficient K2 at temperatures T1 and T2. As shown in FIG. 11, as the temperature T increases, the values of the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 increase. In FIG. 11, for convenience, only temperatures T1 and T2 are shown, but by storing the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 corresponding to each required temperature in the memory unit 53, the optimal first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 can be used according to the ambient temperature of the storage element. Although not shown, the first mode current expansion coefficient M1 and the second mode current expansion coefficient M2 during current flow are also stored in the memory unit 53. Alternatively, the first mode time expansion coefficient and the second mode time expansion coefficient may be formulated as a function of temperature, and a calculation circuit may be used that performs the formulated calculation.

Figure 12 shows the relationship between the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 and ΔSOC. In Figure 12, the horizontal axis shows time (days) and the vertical axis shows the change in cell thickness (%). Figure 12 shows a solid straight line with a slope of the first mode temporal expansion coefficient K1 at ΔSOC1 and ΔSOC2 (>ΔSOC1), and a dashed straight line with a slope of the second mode temporal expansion coefficient K2 at ΔSOC1 and ΔSOC2. As shown in Figure 12, as ΔSOC increases, the values of the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 increase. For convenience, FIG. 12 illustrates only ΔSOC1 and ΔSOC2, but by storing the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 corresponding to each required ΔSOC in the memory unit 53, it is possible to use the optimal first mode temporal expansion coefficient K1 and second mode temporal expansion coefficient K2 according to the ΔSOC of the storage element. Although not shown, the first mode current-flow expansion coefficient M1 and the second mode current-flow expansion coefficient M2 during current flow are also stored in the memory unit 53. Alternatively, the first mode temporal expansion coefficient and the second mode temporal expansion coefficient may be formulated as a function of ΔSOC, and a calculation circuit that performs the formulated calculation may be used.

Figure 13 shows the relationship between the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 and the central SOC. In Figure 13, the horizontal axis shows time (days) and the vertical axis shows the change in cell thickness (%). Figure 13 shows a solid straight line with a slope of the first mode temporal expansion coefficient K1 at the central SOC1 and central SOC2 (> central SOC1), and a dashed straight line with a slope of the second mode temporal expansion coefficient K2 at the central SOC1 and central SOC2. As shown in Figure 13, the values of the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 change depending on the central SOC. For convenience, only the center SOC1 and center SOC2 are shown in FIG. 13, but by storing the first mode temporal expansion coefficient K1 and the second mode temporal expansion coefficient K2 corresponding to each required center SOC in the memory unit 53, it is possible to use the optimal first mode temporal expansion coefficient K1 and second mode temporal expansion coefficient K2 according to the center SOC of the storage element. Although not shown, the first mode current-flow expansion coefficient M1 and the second mode current-flow expansion coefficient M2 during current flow are also stored in the memory unit 53. Alternatively, the first mode temporal expansion coefficient and the second mode temporal expansion coefficient may be formulated as a function of the center SOC, and a calculation circuit that performs the formulated calculation may be used.

The determination unit 56 may determine the transition from the first mode to the second mode depending on the type of at least one of the positive and negative active materials of the storage element. It is considered that the transition time from the first mode to the second mode is different for storage elements with different active materials, even if the usage environment, dimensions, and element structure are the same. In the case of a lithium-ion battery, lithium ions are inserted into or removed from the active material during charging and discharging. Since the shape change speed differs depending on whether the type of at least one of the positive and negative active materials is an active material that has a large or small volume change upon insertion and removal, it is possible to determine the transition time from the first mode to the second mode. For example, when the positive active material is a lithium nickel oxide-based material, the volume change upon insertion and removal is relatively large, so it can be determined that the transition from the first mode to the second mode is relatively fast.

Figure 14 is a flowchart showing the processing procedure for shape estimation by the estimation device 50. For convenience, the following description will be given with the control unit 51 as the main processor. The control unit 51 acquires time series data of the current, voltage, and temperature of the storage element along with time data (S11), and identifies the ΔSOC, median SOC, and average temperature (S12). When the storage element is in an unused state, the ΔSOC, median SOC, and average temperature of the storage element are acquired. When the storage element is in a non-energized state (abandoned state) after being energized, the ΔSOC, median SOC, and average temperature immediately before the non-energized state can be identified.

The control unit 51 calculates the elapsed parameter (S13) and determines whether the calculated elapsed parameter is equal to or greater than a threshold value (S14). If the elapsed parameter is not equal to or greater than the threshold value (NO in S14), the control unit 51 selects the first mode temporal expansion coefficient K1 and the first mode current expansion coefficient M1 (S15) and estimates the shape change (S17).

If the elapsed parameter is equal to or greater than the threshold value (YES in S14), the control unit 51 selects the second mode time-dependent expansion coefficient K2 and the second mode current-dependent expansion coefficient M2 (S16) and performs the process of step S17.

The control unit 51 determines whether or not to end the process (S18). If the process is not to be ended (NO in S18), the process continues from step S13 onwards. If the process is to be ended (YES in S18), the process ends.

When the state of the storage element is a mixture of a current-carrying state and an unused state, the shape can be estimated as the sum of the amount of expansion over time (change in shape when unused) and the amount of expansion with current (change in shape when current is applied) calculated using the coefficients of expansion over time (K1, K2) and the coefficients of expansion with current (M1, M2).

The estimation device 50 can also be realized using a general-purpose computer equipped with a CPU (processor), RAM (memory), etc. That is, the estimation device 50 can be realized on a computer by loading a computer program that defines the procedures for each process, such as that shown in FIG. 14, into a RAM (memory) equipped in the computer and executing the computer program with a CPU (processor). The computer program may be recorded on a recording medium and distributed.

As described above, according to this embodiment, the shape change (thickness change) of the storage element at the end of its life can be estimated during the development and design stages of the storage element, making it possible to design an optimal battery module that takes into account the shape (thickness) of the storage element at the end of its life. This makes it possible to avoid excessive enlargement of the battery module, reduce costs, and achieve maximum battery performance.

In this embodiment, the swelling of the element structure has been mainly described. This embodiment can be similarly applied not only to the swelling of the element structure, but also to the change in shape of the electricity storage element caused by gas generated from the electrolyte during overcharging or the like.
In the present embodiment, the energy storage element has a prismatic cell case (made of, for example, metal). Alternatively, the energy storage element may be a so-called pouch cell that uses a laminate film for the case.

The embodiments are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims.

10 Battery module (electricity storage device)
11 Case 12 Bus bar 13, 14 Lead 20 Cell (electric storage element)
Reference Signs List 21 Cell case 21a, 21b Long side surface 21c, 21d Short side surface 22 Cover plate 23, 26 Terminal 24 Burst valve 25 Electrode body 50 Estimation device 51 Control unit 52 Input unit 53 Memory unit 54 Timer unit 55 Output unit 56 Determination unit 57 Estimation unit 58 Communication unit

Claims (9)

a determination unit that determines whether a shape change mode over time of an energy storage element having a wound electrode body is a first mode or a second mode having a shape change rate different from that of the first mode , based on a predetermined elapsed parameter and a threshold value ;
and an estimation unit that estimates a shape change of the energy storage element that depends on an expansion of an element structure of the energy storage element and an occurrence of wrinkles in the element structure in accordance with the shape change mode determined by the determination unit.
Estimation device. A shape change speed in the second mode transitioned from the first mode is greater than a shape change speed in the first mode.
The estimation device according to claim 1 . A first acquisition unit that acquires or calculates an elapsed parameter related to an elapsed period from a start of leaving the storage element when the storage element is left unused ,
The determination unit is
determining a shape change mode based on the progress parameter acquired or calculated by the first acquisition unit;
The estimation device according to claim 1 or 2 . A second acquisition unit that acquires or calculates a progress parameter related to the energization of the storage element,
The determination unit is
determining a shape change mode based on the progress parameters acquired or calculated by the second acquisition unit;
The estimation device according to any one of claims 1 to 3 . The process parameters are:
The electric storage element includes any one of the number of days elapsed when the electric storage element is not energized or is energized, the absolute value of the dimension of the electric storage element, the amount of change in the shape of the electric storage element, and the total SOC fluctuation amount of the electric storage element.
The estimation device according to claim 3 or 4 . The determination unit is
determining whether the power storage device is to transition from the first mode to the second mode in accordance with at least one of the types of a positive electrode active material and a negative electrode active material of the power storage device;
The estimation device according to any one of claims 1 to 5 . The shape change includes a change in thickness of the wound electrode body.
The estimation device according to claim 1 . On the computer,
determining whether a shape change mode of an energy storage element having a wound electrode body over time is a first mode or a second mode having a shape change rate different from that of the first mode based on a predetermined elapsed parameter and a threshold value ;
estimating a shape change of the energy storage element due to expansion of an element structure of the energy storage element and occurrence of wrinkles in the element structure according to the determined shape change mode;
A computer program that executes a process. determining whether a shape change mode of an energy storage element having a wound electrode body over time is a first mode or a second mode having a shape change rate different from that of the first mode based on a predetermined elapsed parameter and a threshold value ;
estimating a shape change of the energy storage element due to expansion of an element structure of the energy storage element and occurrence of wrinkles in the element structure according to the determined shape change mode;
Estimation method.

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